Speed control systems have been heretofore known and utilized, particularly in association with manually actuated revolving doors, with the purpose of such systems being to limit the rate of motion, or rotation, of the door. Such devices as have been heretofore known have typically employed oppositely directed spinning masses mounted on guide pins to a carrying member connected to the shaft so that the masses and the shaft rotate within a brake drum. A standard gear train is connected with the shaft and with the centrally rotating rod of the revolving door in order to develop the mechanical advantage necessary to deliver the proper amount of braking torque to the revolving door (for example the rotation of the door being related to the rotation of the shaft at a ratio of about 1 to 100). The rotating masses have been heretofore biased inwardly by a pair of springs each one of which is connected between the rotating masses at different sides thereof.
While such heretofore known speed control systems have met with some acceptance, such systems have not proven completely successful, and in particular have proven difficult to adjust and/or maintain in proper adjustment to provide desired engagement of the rotating masses with the brake drum. The shaft speed at which the masses engage the drum depends primarily on the total spring preload force (i.e., the sum of the preloads on each of the individual springs between the rotating masses), and in such known two spring systems it has heretofore been necessary that the preload force of the two springs be essentially the same in order to prevent binding of the masses on the guide pins.
Furthermore, such known devices have not always proven effective where, for example, the friction material utilized on the rotating masses becomes lubricated, for example by water seeping through joints in, or lubricants maintained within, the housing. Further improvements in such speed control systems could thus still be utilized.